| Summary: | This paper proposes a new optical configuration for a two-axis surface encoder that can measure the in-plane (<i>X</i>-axis) and out-of-plane (<i>Z</i>-axis) displacements of a positioning stage. The two-axis surface encoder is composed of a scale grating and a sensor head. A transparent grating is employed in the sensor head for measurement of the <i>Z</i>-directional displacement of the scale grating based on the Fizeau-type measurement method; a reference beam reflected from the transparent grating and the zeroth-order diffracted beam from the scale grating are superimposed to generate an interference signal. A pair of prisms and a beam splitter are also employed in the sensor head, so that the positive and negative first-order diffracted beams can be superimposed over a long working distance to generate an interference signal for measurement of the <i>X</i>-directional displacement of the scale grating. Focusing on the new, extended <i>Z</i>-directional measurement mechanism, proof-of-principle experiments were carried out to verify the feasibility of the proposed optical configuration for the surface encoder that can measure the uni-directional displacements of a scale grating along the <i>X</i>- and <i>Z</i>-axis. Experimental results from the developed optical configuration demonstrated the achievement of a <i>Z</i>-directional measuring range of ±1.5 mm.
|
|---|